Cellulosic organic solvent soluble products

ABSTRACT

The invention provides an improved cellulosic ester or ether product with a degree of substitution of between 2.0 and about 2.9 which is derivatized or further reacted by reaction with an acrylamide reactant to substitute to a D.S. of from about 0.05 to about 0.5 and provide a hydroxyl D.S. of from about 0.05 to about 0.5, and thereby provide a polymerizable organic solvent-soluble product which is insoluble in water and copolymerizable with vinyl monomers. The product is prepared by reacting a cellulose derivative with a catalyst and the acrylamide reactant at a pH of from between about 4.2 and about 4.5. The reaction is carried out at a temperature between 80° C. and 120° C. for from one-half to three hours, while removing the water of reaction.

The present invention relates generally to improved cellulosic ester orether products with a degree of substitution of between 2.0 and about2.9 and derivatized or further reacted by reaction with an acrylamidereactant to substitute to a D.S. of from about 0.05 to about 0.5 andprovide a hydroxyl D.S. of from about 0.05 to about 0.5 and also providea polymerizable organic solvent-soluble product which is insoluble inwater and copolymerizable with monomers.

BACKGROUND OF INVENTION

Cellulosic products are extensively used for a variety of non-food andindustrial applications. Products prepared from starch and cellulosehave traditionally been used to size or finish textiles and papers; asadhesives in corrugated and laminated paperboards, remoistening gums,and wallpapers; as flocculants; as binders, as for example in foundrycore binders; fabric aids; thickeners; and many other applications.Cellulose esters and ethers have been used as plastics for molding,coatings, extrusion and laminates.

Cellulose derivatives have not provided good overall substitutes forsynthetic polymeric materials which are primarily produced frompetrochemical raw materials. Much effort has been undertaken towards thedevelopment of new techniques which would enable the art to usecellulose-based products as a synthetic polymer replacement inapplications requiring little or no water-sensitivity. The art hascontinued to search for effective cellulose-based products for syntheticpolymer replacement.

In general, the prior art has provided cellulose acylamides which havewater-sensitivity and/or which have not functioned to a high degree as asubstitute for synthetic polymeric materials produced from petrochemicalraw materials. Indeed, the reaction of cellulose with acrylamides is nowwell-known and acrylamidomethyl cellulose has been described in the art.Likewise, acryloyl, methacrylyl and crotonic esters of cellulose acetatehave been disclosed in the prior art. The reaction of cellulose withN-methylolamides such as methylol ureas, methylol melamines, andmethylol cyclic ureas are documented and lead to products which arecross-linked and insoluble. These products have generally found use inthe textile industry to provide articles which should retain a permanentshape.

However, the prior art has not found polymerizable organicsolvent-soluble cellulose products which are insoluble in water andwhich are copolymerizable with vinyl monomers, which can be effectivelyused as coatings, and which can provide more effective substitutes forsynthetic polymeric materials primarily produced from petrochemical rawmaterials. It is recognized as being desirable to have such effectivesubstitutes which can be derived from readily available andreplenishable crops each year.

OBJECTS

The principal object of this invention is to provide improved cellulosicproducts which are polymerizable and organic solvent-soluble.

Another object of the invention is to provide an improved cellulosicester or ether which can more effectively substitute for syntheticpolymeric materials which are produced from petrochemical raw materials.

A still further object of the invention is the provision of a cellulosicderivative which is self-cross-linkable, organic solvent-soluble, andwhich is copolymerizable with vinyl monomers and which is useful incoatings, adhesives, plastics, and other applications.

Further objects and advantages of this invention will appear from thefollowing disclosure.

DESCRIPTION OF THE INVENTION

The invention is directed to the provision of an improved cellulosicproduct prepared from a cellulosic derivative which has been derivatizedto a degree of substitution (D.S.) of between about 2.0 and about 2.9 byreaction with an acrylamide reactant to substitute the acrylamide in thecellulosic derivative to a degree of substitution (D.S.) of from about0.05 to about 0.5 and provide a product having a hydroxyl (OH) degree ofsubstitution (D.S.) of from about 0.05 to about 0.5. The improvedcellulosic product provides a polymerizable and copolymerizable organicsolvent-soluble product which is insoluble in water and which iscopolymerizable with many monomers.

The water insoluble cellulose is characterized by having the hydroxylgroups substituted to a degree of substitution of more than about 2.0and less than 3.0. The cellulose useful in this invention has beenreacted to provide an ester or ether with a hydrophobic substituentwhich is substituted in the cellulose to a D.S. of between about 2.0 andabout 2.9 thereby leaving hydroxyl at a D.S. of 0.1 to 1.0. Thehydrophobic substituent preferably has a carbon chain length of from C₂to C₇ and may be aliphatic or aromatic. The resulting ester or ether isreacted with an acrylamide to substitute it to a D.S. of between about0.05 to about 0.5 leaving the hydroxyl at a D.S. of between about 0.05and about 0.5 in the product of the invention.

The acrylamide reactants include N-methylol and N-methylthio acrylamidessuch as N-(hydroxymethyl)acrylamide;N-(hydroxymethyl)-N-[(1-hydroxymethyl)propyl]acrylamide;N-(hydroxymethyl-2-alkyl acrylamides, (e.g.N-(hydroxymethyl)-2-(methyl-heptyl)acrylamide;N-[(hydroxymethyl)-1-nonyl]-2-methyl acrylamide;N-(1-hydroxymethyl)-2-methyl acrylamide; N-(hydroxymethyl)-2-propylacrylamide; etc.) N-(mercaptomethyl)acrylamide; N-methylol-N-isopropylacrylamide; 3-(N-methylol acrylamido)-3-methyl butyl trimethyl ammoniumchloride (cationic); sodium-2-N-methylol acrylamido-2-methyl propanesulfonate (anionic-CH₂ :C(H)C(:O)N(CH₂ OH)C(CH₃)₂ CH₂ SO₃ -NA+),combinations thereof and the like.

In the method of the invention, the water-insoluble cellulosicderivative is first prepared, but it may be purchased in themarketplace. The derivative will have a D.S. of between 2.0 and about2.9, and preferably between 2.4 and 2.8. The cellulosic derivative ismixed with a catalyst, such as ammonium chloride, and an acrylamidereactant. The pH should be in the range of between about 4.2 and about4.5. The acrylamide reactant may be in a dry form or may be in asolution of water or suitable solvent.

A polymerization inhibitor such as methyl hydroquinone is optionallyincluded in the reaction, as well as a swelling agent, such as ethyleneglycol, propylene glycol, or N-methyl pyrrolidone.

Water or solvent may then be removed from the mixture under conditionswhich will not cause the acrylamide reactant to polymerize or react.Temperatures below 80° C. are preferred and vacuum-drying, oven-dryingor similar conditions may be employed. It will be understood, however,that moisture or solvent may be present during reaction. The mixture maybe spread in a thin layer for drying to a free-flowing powder. The driedmixture is then milled if necessary and reacted in the temperature rangeof 80° C. to 120° C. for from about one-half to about three hours. It isimportant to effect removal of water formed during reaction. The reactedproduct may be washed by suspending in water, and neutralized to pH 5-6.The reacted product is filtered and washed until free of catalyst. Therecovered product is dried and should have a nitrogen content equivalentto the acrylamide reactant used at the desired degree of substitution.The measurement of the nitrogen content can be used to determine thatthe desired degree of reaction has occurred. When usingN-methylolacrylamide, the nitrogen content of the recovered product willbe between about 0.2 and about 2%. The end product is soluble in organicsolvents and vinyl monomers, and well-adapted to self-polymerization andcopolymerization reactions.

The products of the invention may be utilized by homopolymerization orcopolymerization to prepare solvent-insoluble internally plasticized,controlled swelling, modified films, coatings, inks, castings,adhesives, membranes and compositions. Polymerization may be effected byradiation as with ultraviolet light, white light, or electron beam, andthermal-curing techniques. Generally, the products can be demonstratedto be compatible with petrochemical-based monomers, oligomers and resinsin curable films, coatings, inks, castings, adhesives, membranes andcomposites. The coatings are effective on wood, paper, metal andplastics so that they are utilizable on containers, furniture, floors,equipment and machinery, appliances, automobiles, trucks, pipe, boats,paper products, and wire as insulation.

ABS, acrylic, polyacrylonitrile, alkyds, diallylphthalate, phenolic,polyester, polystyrene, PVC resins can be modified by copolymerizationor compounding with the products of the invention. The compatibility ofthe products of the invention with many monomers readily leads to theformation of a large number of polymers.

A film can be prepared by mixing an acrylamidomethyl cellulose acetatebutyrate with ethylacrylate at various levels and a photo-initiator, andspreading the mixture on a treated metal base such as sheets sold underthe trademark, Bonderite 37. Curing can be effected by ultraviolet lightin a short time to provide various desirable physical propertiesincluding elongation, reverse impact, tensile strength, and elasticmodulus.

Castings of copolymers of the products of the invention with ethylacrylate, butyl acrylate, methyl methacrylate and styrene show low-waterabsorbence.

Homopolymerization can be effected by solubilizing the products of theinvention in a low-boiling organic solvent, such as acetone, in thepresence of an initiator, such as benzoyl peroxide, with thermal cure.

Various adhesive formulations may be prepared with the products of theinvention. For example, a product may be mixed with 2-hydroxyethylacrylate and acetone along with benzoyl peroxide and dimethyl aniline toprovide an adhesive which strongly bonds to birchwood, glass andaluminum.

EXAMPLE 1

First, 2,070 gm of deionized water were placed in a 19-liter batteryjar, and 138 gm of ammonium chloride and 19.9 gm of p-methoxyphenol wereadded. The ingredients were stirred vigorously with stainless steelstirrers and impellers until the ammonium chloride and p-methoxyphenolbecame dissolved. Next, 1,857 gm of N-methylolacrylamide, as a 48-weightpercent aqueous solution, was added with continued stirring. Then 3,000gm, on a dry solids basis (dsb), of cellulose acetate butyrate, sold byEastman Chemicals under the designation, CAB 551-0.01, was slowly addedand mixed in. The cellulose acetate butyrate had a viscosity of 0.1seconds; an acyl content of 2.0% acetyl and 53% butyryl; and a hydroxylcontent of 1.5%. The D.S. was 2.76. The pH was determined and adjustedto the range of between 4.2 and 4.5. Stirring was continued for one anda half hours and the slurry then filtered. The resulting filter cake waswashed with a portion of the filtrate and the "wet cake" was transferredto steel trays. The product was air-dried in a well-ventilated hood forabout two days to a moisture content to about 4% to form a reactivepremix.

After air-drying, the premix was placed on stainless steel trays andreacted for one hour at 100° C. in an oven. The reacted product was thencooled to room temperature in a well-ventilated hood.

The reacted product was then slurried in deionized water and the pHdetermined to be 3.5. This pH was adjusted to 5.5 with dilute sodiumhydroxide. The slurry was stirred for about eight hours and thenfiltered. Washing was continued until the filtrate was free of chlorideion. The product was then washed with fifty w/w percent aqueous ethanol(3A) and was suspended overnight in the aqueous ethanol. The reactedproduct was again filtered and washed with deionized water to removeresidual alcohol. The product was again transferred to a tray and driedat about 55° C. until a moisture level of about 2% was reached. Theproduct had 0.4% nitrogen. The D.S. of the acrylamide was 0.11 and thehydroxyl was 0.13.

The product is a dry, free-flowing, white to off-white powder, which isuseful in producing tough, hard, high-gloss, durable copolymerizates.

The product is useful for reactive coatings and inks copolymerized withmonomers, drying oils, unsaturated polyesters, and/or alkyd resins toproduce high molecular weight useful films. The product had a meltingpoint of 110° C. to 125° C., provided rheological control to minimizerunning and sagging, improved inter-coat adhesion, eliminated cratering,and reduced dry-to-touch time. The product copolymerizes vinyl monomervehicles both thermally and photochemically, and does not homopolymerizeduring storage.

The product had a Brookfield viscosity of 220 cps at 40 weight percentin methyl ethyl ketone at 25° C.

The product is soluble at 40 weight percent in the following:

    ______________________________________                                        Methyl acrylate                                                               Ethyl acrylate                                                                Butyl acrylate                                                                Methyl methacrylate                                                           Vinyl acetate                                                                 Vinylidene chloride                                                           Styrene                                                                       Styrene:methyl methacrylate                                                                        80:20                                                    2-Hydroxyethyl acrylate                                                       N--vinyl pyrrolidone                                                          Styrene:methanol     80:20                                                    ______________________________________                                    

The hydroxyl content, calculated as weight percent, was 1.1% OH. Theacid value was zero, and the D.S. of the vinyl group was 0.11.

EXAMPLE 2

A portion of the "wet cake" from Example 1 was dried in a 60° C. ovenfor about five hours to a moisture of about 4%. The oven-dried reactionmixture was then placed on a stainless steel tray and reacted forseventy-five minutes in an oven at 100° C. The reacted product wasslurried in deionized water and the pH was adjusted to 5.5 with dilutesodium hydroxide. The slurry was stirred for an hour, filtered andwashed free of the catalyst. The product was then washed with fifty w/wpercent aqueous ethanol (3A) and was suspended overnight in the aqueousethanol. The product was filtered, washed with deionized water to removethe alcohol and dried at 55° C. until a moisture of less than 2% wasreached. The product contained 0.43% nitrogen. The acrylamide D.S. was0.11 and the hydroxyl 0.14.

EXAMPLE 3

Cellulose acetate D.S. 2.76 (100.5 gm; formula weight 265.6); 43 gm 48%(w/w/) of N-methylolacrylamide; 3.43 gm of ammonium chloride, and 0.33gm of p-methyl hydroquinone were mixed in 284 gm of water. The mixturewas stirred for 1.5 hours, filtered and 222 gm of filtrate was collectedfor a retention of 33% of the aqueous phase in the cellulose acetate"wet" reaction premix. The "wet" premix (76.6 gm; 50% moisture) wasplaced on a stainless steel tray and reacted in a 110° C. oven for twohours and thirty-five minutes. The crude product was suspended in 100ml. of water with stirring. The pH was adjusted from 3.65 to 6.0 with0.5N aqueous sodium hydroxide. After filtering, washing free of catalystand drying at 55° C. the product had a nitrogen content of 0.54% (0.11D.S.).

The corresponding reaction premix was air-dried to 12% moisture. It wasreacted 1.5 hours at 110° C. and yielded a product which contained 0.54%nitrogen (0.11 D.S.).

EXAMPLE 4

Two hundred gm of cellulose acetate (formula weight 265.6) was placed ina 2-liter single-neck distilling flask. The flask was attached to aBuchi Rotavapor unit and rotated. The pressure was reduced to 5 inchesof vacuum and 24.7 gm of a water solution of 10.8 gm ofN-methylolacrylamide, 2 gm of ammonium chloride and 0.2 gm of methyhydroquinone was added through an inner Teflon delivery tube of theRotavapor. The reactant mixture was followed by 8.5 gm of water as awash for the delivery tube. The vacuum was released and the mixture inthe rotating flask was tumbled for one hour. Small "wet" layers on thesides of the flask next to the neck and the bottom were scraped off.Some glass beads and pieces of glass tubing (5 mm long and 5 mmdiameter) were added to the blend to break soft aggregates. The blendingwas continued for two hours. The glass beads and tubing were removed bypassing the solid through a 20-mesh screen (with no shaking).

The wet reaction mix (103.5 gm) was placed in a one-liter single-neckflask and the flask was attached to the Buchi Rotavapor. The flask wasevacuated to 28 inches vacuum and, while rotating, was immersed in a110° C. oil bath for two hours. The water was collected in dry icetraps. The product tumbled freely during the reaction. The reactionmixture was suspended in 280 ml. of water and the pH was adjusted from3.5 to 6.0 with 0.5N sodium hydroxide solution. The product wasfiltered, washed free of catalyst and other by-products and dried at 50°C. The nitrogen content was 0.51% (0.10 D.S.). A portion of the abovepremix was reacted in a 110° C. forced-air oven for 1.5 hours. Thenitrogen content of the product was 0.54% (0.106 D.S.).

EXAMPLE 5

An acrylamidomethyl cellulose acetate was prepared at a 0.5% nitrogenlevel by the method of Example 1 except that the ingredients comprise:

    ______________________________________                                        Cellulose acetate,    2,500 gm (dsb)                                          N--methylolacrylamide, 48%                                                                          1,067 gm                                                Ammonium chloride     81.8 gm                                                 Methoxyphenol         8.3 gm                                                  Water, deionized      7,083 gm                                                ______________________________________                                    

The cellulose acetate was obtained from Eastman Chemicals and identifiedas CA-398-3. The viscosity measured 11.4 poises. The acetyl content was39.8% and the combined acetic acid analyzed 55.5%. The hydroxyl contentmeasured 3.5%. The cellulose acetate had a D.S. of 2.46.

The product was a dry, free-flowing, white to off-white powder producingtough, hard, high-gloss durable copolymerizates.

The powder had a Brookfield viscosity at 30 weight percent level inmethyl ethyl ketone at 25° C. of 13,000 cps.

The product was soluble at 20 weight percent in:

    ______________________________________                                        N--Vinyl pyrrolidone                                                          2-Hydroxyethyl acrylate                                                       Acrylic acid                                                                  Ethyl acrylate:N--vinyl pyrrolidone                                                                     80:20                                               Methyl methacrylate:N--vinyl pyrrolidone                                                                80:20                                               Styrene:N--vinyl pyrrolidone                                                                            50:50                                               Ethyl acrylate:2-Hydroxyethyl acrylate                                                                  80:20                                               Methyl methacrylate:2-Hydroxyethyl acrylate                                                             80:20                                               Styrene:2-Hydroxyethyl acrylate                                                                         50:50                                               ______________________________________                                    

Hydroxyl content, calculated as weight percent, was 3.2%; the acid valuewas zero and the D.S. of the vinyl group was 0.11. The nitrogen contentwas 0.5%. The product is useful in making a thermal-cured film and inadhesive formulations. It also exhibited monomer solubility.

EXAMPLE 6

Acrylamidomethyl cellulose acetate butyrate was made at a 0.4% nitrogenlevel in accordance with Example 1, except that the ingredientsincluded:

    ______________________________________                                        Cellulose acetate butyrate                                                                            3,000 gm                                              N--methylolacrylamide, 48%                                                                            1,521 gm                                              Ammonium chloride       55 gm                                                 p-methoxyphenol         5.5 gm                                                Water                   791 gm                                                ______________________________________                                    

The cellulose acetate butyrate was obtained from Eastman Chemicals andidentified as CAB 381-1. It had a viscosity of 0.38 poises. The acetylcontent was 13.0% and the butyryl content was 37%. The hydroxyl contentwas 1.0%. The total D.S. was 2.73 of substitution.

The product had compatibility with the following monomers at 40 weightpercent with the indicated clarity as follows:

    ______________________________________                                        Methyl acrylate       clear                                                   Ethyl acrylate        slight haze                                             Butyl acrylate        clear                                                   Methyl methacrylate   clear                                                   Vinyl acetate         slight haze                                             Vinylidene chloride   clear viscous fluid                                     Styrene                                                                       Styrene/methyl methacrylate (80/20)                                                                 clear                                                   Styrene/methanol (80/20)                                                                            clear                                                   ______________________________________                                    

EXAMPLE 7

An acrylamidomethyl ethyl cellulose was prepared from three grades ofethyl cellulose identified as N-4; N-7; and K-14 obtained from Hercules,Inc. The characteristics of the product were as follows:

    ______________________________________                                                     N-4      N-7     K-14                                            ______________________________________                                        Viscosity, cps (5%                                                                           5          6.8     14                                          wt. soln. in 80/20                                                            (wt) toluene/ethanol                                                          Ethoxyl        48.4       48.9    46.4                                        Estimated Formula                                                                            231.7      232.8   227.8                                       weight                                                                        ______________________________________                                    

The D.S. of the products were 2.49, 2.53, and 2.35 respectively.

Premixes of the following ingredients were prepared as follows:

    ______________________________________                                        Ethyl cellulose,                                                                            58.8(58)   58.9(58) 58.2(58)                                    as is, (dry), gm                                                              N--methylol-  26.9(12.9) 24.8(11.9)                                                                             34.2(16.4)                                  acrylamide, 48%                                                               in water, (dry), gm                                                           NH.sub.4 Cl (0.1 g/ml                                                                       12         12       12                                          H.sub.2 O), ml                                                                N--methyl-    10         10       10                                          pyrrolidone, ml                                                               Methyl hydro- 0.01       0.01     0.01                                        quinone, gm                                                                   Water, gm     25         20       25                                          ______________________________________                                    

The premixes were mixed and the resulting semi-fluid mass was layeredonto a flat tray and air-dried as a relatively thin layer until themoisture level was about 10%. The dried product was powdered andblended.

Each of the formulations was reacted at one and two hours at 93° C. and103° C., whereupon they were suspended in water and the pH adjusted to5.5. The filter cake was washed with water until free of chloride ionand the product then dried.

One gram each of the dry products was dissolved in 5 ml of toluene.Polymerizations were carried out at 70° C. for 16 hours with 25 mgazobis (isobutyronitrile) initiator. The gels were extracted repeatedlywith toluene and the solubles in the combined washes determined.

    __________________________________________________________________________    Reaction                                                                              N-4       N-7       K-14                                              Temp. °C.                                                                      93   103  93   103  93   103                                                  % Nitrogen (N)                                                                % Solids (S)                                                          Reaction                                                                      Time, Hr.                                                                             N  S N  S N  S N  S N  S N  S                                         __________________________________________________________________________    1       0.51                                                                             46                                                                              0.50                                                                             32                                                                              0.59                                                                             20                                                                              0.46                                                                             14                                                                              0.94                                                                             9 0.73                                                                             8                                         2       0.58                                                                             33                                                                              0.55                                                                             34                                                                              0.59                                                                             17                                                                              0.43                                                                             16                                                                              1.0                                                                              13                                                                              0.75                                                                             9                                         __________________________________________________________________________

The products are soluble in acetone, toluene, N-methylpyrrolidone, ethylacetate, tetrahydrofuran, chloroform. It is soluble in various monomers.

The various features of the invention which are believed to be new areset forth in the following claims.

What is claimed is:
 1. A polymerizable cellulosic ester or ether productcapable of homopolymerization having a degree of substitution of between2.0 and about 2.9 reacted with an acrylamide reactant containing amethylol group to substitute to a degree of substitution of from about0.05 to about 0.5 and provide a hydroxyl degree of substitution of fromabout 0.05 to about 0.5.
 2. A cellulosic product in accordance withclaim 1 which is organic solvent-soluble and copolymerizable with vinylmonomers.
 3. A cellulosic product in accordance with claim 1 having adegree of substitution of between 2.4 and 2.8.
 4. A cellulosic productin accordance with claim 1 in which the acrylamide reactant containing amethylol group is selected from the group consisting of N-methylol andN-methylthio acrylamides such as N-(hydroxymethyl)acrylamide;N-(hydroxymethyl)-N-[(1-hydroxymethyl)propyl]acrylamide;N-(hydroxymethyl)-2-alkyl acrylamides, (e.g.,N-(hydroxymethyl)-2-(methylheptyl)acrylamide;N-[(hydroxymethyl)-1-nonyl]-2-methyl acrylamide;N-(1-hydroxymethyl)-2-methyl acrylamide; N-(hydroxymethyl)-2-propylacrylamide; N-(mercaptomethyl)acrylamide; N-methylol-N-isopropylacrylamide; 3-(N-methylol acrylamido)-3-methyl butyl trimethyl ammoniumchloride (cationic); sodium-2-N-methylol acrylamido-2-methyl propanesulfonate (anionic-CH₂ :C(H)C(:O)N(CH₂ OH)C(CH₃)₂ CH₂ SO₃ Nacombinations thereof.
 5. A product in accordance with claim 1 in whichthe cellulosic product is derived from cellulose acetate.
 6. A productin accordance with claim 1 in which the cellulosic product is derivedfrom cellulose acetate butyrate.
 7. A product in accordance with claim 1in which the cellulosic product is derived from ethyl cellulose.
 8. Aproduct in accordance with claim 1 in which the cellulosic product isderived from cellulose acetate proprionate.
 9. A product in accordancewith claim 1 in which the cellulosic product is derived from cellulose2-cyanoethyl ether.
 10. A product in accordance with claim 1 in whichthe acrylamide reactant is N-methylolacrylamide.
 11. A product inaccordance with claim 1 in which the acrylamide reactant isN-methylolmethacrylamide.
 12. A method for preparing a polymerizablecellulosic ester or ether product capable of homopolymerizationcomprising the steps of providing a cellulosic derivative having adegree of substitution of between 2.0 and about 2.9, mixing saidderivative with a catalyst and an acrylamide reactant containing amethylol group, adjusting the pH to between about 4.2 and about 4.5, andthen heating the mixture to a temperature of between 80° C. and 120° C.for from one-half to three hours while removing water of reaction fromthe mixture.
 13. A method in accordance with claim 12, wherein the waterof reaction is removed as it is formed.
 14. A method in accordance withclaim 12 wherein the product is washed after reaction.
 15. A method inaccordance with claim 12 wherein the mixture is dried under vacuum priorto reaction.
 16. A method in accordance with claim 15 wherein the dryingis carried out at temperatures below reaction temperatures.